Zn-Templated synthesis of substituted (2,6-diimine)pyridine proligands and evaluation of their iron complexes as anolytes for flow battery applications

Abstract

Zn2+ templating enables synthesis of redox ‘non-innocent’ diimine pyridine ligands with strong electron-withdrawing groups, allowing construction of iron complexes with multiple ligand-based reductions for application in redox flow batteries.

Diiminepyridine‐Supported Phosphorus(I) and Phosphorus(III) Complexes: Synthesis, Characterization, and Electrochemistry

“…As befits the ability to isolate both P (I) and P (III) congeners, (irreversible) oxidation of [( dipp DIP t Bu )P][BPh 4 ] is observed electrochemically at ≈ +0.4 V vs. FcH 0/+ (FcH = ferrocene; Figure ). Interestingly, the complex also shows a reversible reduction at –1.38 V. This cathodic event is consistent with ligand‐based reduction, common for diiminepyridine complexes of metals , . However, one could also postulate the reduction as forming a formally neutral P (0) complex.…”

Delocalization tunable by ligand substitution in [L2Al]n−complexes highlights a mechanism for strong electronic coupling

“…There is an expected anodic shift in redox events upon changing the ligand from ED 1 or 3 to EW 2 ; for example the E 1/2 for the A 0/1− redox couple is at 0.06 V vs. SCE for 1 and shifted by −140 and +470 mV for 3 and 2 , respectively. 29,30 At very negative potentials 2 and 3 show signs of decomposition over time.…”

Octahedral Iron Complexes of Pyrazine(diimine) Pincers: Ligand Electronic Effects and Protonation

“…Qualitatively similar redox features for the pyridine­(diimine) iron complexes [( 4‑OMe PDI) 2 Fe] 2+ and [( 4‑ t Bu PDI) 2 Fe] 2+ have been reported; both complexes show two reversible ligand-based reductions at −1.3 and −1.6 V and a metal centered oxidation near +0.9 V vs Fc/Fc + in acetonitrile. , The shift of the first reduction and oxidation to more positive potentials can likely be attributed to the increased electron affinity and π-acidity of the pyrazine moiety. We note that the redox potentials of this class of compounds can also be affected by the substituents on the imine N-aryl rings; for instance, para -substitution of the N-aryl rings of bis­(diiminopyridine) iron complexes with electron-withdrawing bromine or nitrile substituents has been reported to shift the first reduction potential to −1.15 and −1.01 V vs Fc/Fc + , respectively, much closer to the values we observe . Therefore, modification of the central ring as well as the N-aryl rings provides multiple avenues to tune the redox properties of pyrazine­(diimine) and pyridine­(diimine) ligands.…”

“…We note that the redox potentials of this class of compounds can also be affected by the substituents on the imine N-aryl rings; for instance, para-substitution of the N-aryl rings of bis(diiminopyridine) iron complexes with electronwithdrawing bromine or nitrile substituents has been reported to shift the first reduction potential to −1.15 and −1.01 V vs Fc/Fc + , respectively, much closer to the values we observe. 37 Therefore, modification of the central ring as well as the N-aryl rings provides multiple avenues to tune the redox properties of pyrazine(diimine) and pyridine(diimine) ligands.…”